A rotary molding machine of the type described herein includes one configuration which has a construction in which a base plate is secured upwardly relative to a machine bed, and an injection molding device which is movable up and down with respect to a transfer plate provided intermittently and rotatably on the underside of the base plate. The injection molding device is movable up and down to effect a clamping action. The other configuration has a construction in which an injection molding device is secured on one side thereof to one side of a machine bed, a base plate side is disposed movably up and down in opposed relation thereto, and a rotary plate is movable down together with the base plate to effect clamping.
The first machine configuration in which the base plate and the transfer plate are fixed has problems that since the injection mold device is moved up and down an every injection molding of a preform, an injection nozzle needs to be separated every time and therefore starting of measurement of resins material is delayed; and drooling or wire-drawing occurs every time the injection nozzle is separated, to a degree which depends on the type of resin. As a result, marginal portions of the injection nozzle or mold gate become stained and in addition a sprue gate is damaged by the resins adhered to the injection nozzle.
The second machine configuration, in which the base plate side is moved up and down, has been developed in order to solve such problems. However, this molding machine involves the problem that the transfer plate, the driving device therefor and various other devices required for molding are also moved up and down together with the base plate. Therefore, the weight which has to be moved vertically is large and as the molding machine becomes large in size, the vertical moving speed is restricted, making it difficult to open and close the lip mold at high speed. Particularly, when the vertically-moving stroke increases, the downwardly moving speed is accelerated so that the lip mold collides with the mold, thus requiring a buffer means. An improved injection orientation blow molding machine for hollow molded products, e.g. bottles, which are longitudinally long has been needed for some time.